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2557 Background: The development of human intratumoral therapy (HIT-IT) has surged as a promising strategy to overcome resistance to checkpoint inhibitors (CPI), promoting a stronger tumor-specific immune response while reducing systemic exposure. A broad variety of agents (i.e: oncolytic viruses, toll-like receptors agonists) administered both in superficial- and deep-seated lesions are being currently tested in clinical trials (CT). Due to the local intervention on tumors, radiological assessment by standard RECIST is challenging and new methods of response that capture and integrate the local and systemic response to HIT-IT are needed. We aimed to evaluate the feasibility and clinical utility of itRECIST (Goldmacher et al., 2020) in patients (pts) treated with HIT-IT in early phase CT. Methods: Retrospective analysis of a cohort of pts with different solid tumor types enrolled in CT including HIT-IT in our institution between August’18 and January’21. Clinical characteristics were collected. Efficacy in target-injected (T-I) and target-non-injected (T-NI) lesions was assessed by objective response rate (ORR) and disease control rate (DCR), as per itRECIST. Overall disease ORR and DCR were assessed per RECIST 1.1/iRECIST. Treatment-related adverse events (TRAEs) were assessed with CTCAE v.5.0. ORR was calculated with Clopper-Pearson method. Survival analysis was made using Kaplan-Meier method. Results: A total of 37 pts were included. Median age was 66 years, 19 pts (51%) were male, all pts had ECOG 0-1. 24 pts (65%) were CPI-naïve. Median previous lines of therapy was 2 (range [r]: 0-11). All pts (100%) received minimum 1 dose of HIT-IT. 6 pts (16%) were treated with monotherapy and 31 pts (84%) in combination with CPI. Median HIT-IT and CPI doses administered were 4 (r: 1-9) and 2 (r: 1-13), respectively. Injected lesions: cutaneous (16.2%), subcutaneous (21.6%), lymph node (32.4%), liver (29.7%). Median size of T-I lesions was 40 mm (r: 19-260). At data cutoff, 32 pts were evaluable. Median follow-up was 14.4 weeks (r: 1.0-81.1). Per RECIST 1.1, overall ORR was 6% (95% CI, 5-7) and DCR was 38% (95% CI, 21-56). Per itRECIST, ORR was 19% (95% CI, 7-36) and DCR was 63% (95% CI, 44-79) in T-I lesions (n = 32), and 10% (95% CI, 22-27) and 48% (95% CI, 29-67) in T-NI lesions (n = 29). Mean decrease in responding T-I and T-NI lesions was -47% (r: -21 to -100) and -41% (r: -26 to -59), respectively. No non-target (NT) lesion was injected. Median progression-free survival was 7.4 weeks (95% CI, 6.6 – 8.2). Median overall survival was 10.0 months (95% CI, 2.3 – 17.7). Incidence of TRAE was 58% (grade 1-2 IT-related pyrexia 43%; grade 3-4, 5%). No treatment-related deaths were recorded. Conclusions: ItRECIST is feasible to implement and adds precision to the radiological assessment of local and distant anti-tumor activity of HIT-IT. No safety issues were detected in our cohort.

Cerebral microdialysis is widely used in neurocritical care units. The goal of this study was to establish the reference interval for the interstitial fluid concentrations of energy metabolites and glycerol by using the extrapolation to zero-flow methodology in anesthetized patients and by constant perfusion at 0.3 µL/min in awake patients. A CMA-71 probe was implanted during surgery in normal white matter of patients with posterior fossa or supratentorial lesions, and the perfusion flow rate was randomized to 0.1, 0.3, 0.6, 1.2, and 2.4 µL/min. Within 24 h of surgery, perfusion was restarted at a constant 0.3 µL/min in fully awake patients. The actual interstitial fluid metabolite concentrations were calculated using the zero-flow methodology. In vitro experiments were also conducted to evaluate the reproducibility of the in vivo methodology. Nineteen patients (seven males) with a median age of 44 years (range: 21–69) were included in the in vivo study. The median (lower–upper) reference interval values were 1.57 (1.15–4.13 mmol/L) for glucose, 2.01 (1.30–5.31 mmol/L) for lactate, 80.0 (54.4–197.0 µmol/L) for pyruvate, and 49.9 (23.6–227.3 µmol/L) for glycerol. The reference intervals reported raises the need to reconsider traditional definitions of brain metabolic disturbances and emphasize the importance of using different thresholds for awake patients and patients under anesthesia.

3032Background: HPD with ICIs has been recently described as progression disease (PD) by RECIST with a ≥ two-fold increase in tumor growth rate experimental vs. reference. However, the implementati...